Understanding how dietary intakes vary over the course of the school day can help inform targeted school-based interventions, but little is known about the distribution or determinants of school-day dietary intakes in Canada. This study examined differences between school-hour and non-school-hour dietary intakes and assessed demographic and socioeconomic correlates of school-hour diet quality among Canadian children. Nationally representative data from the Canadian Community Health Survey were analyzed using 24-h dietary recalls falling on school days in 2004 (n = 4827). Differences in nutrient and food-group densities during and outside of school hours and differences in School Heathy Eating Index (School-HEI) scores across sociodemographic characteristics were examined using survey-weighted, linear regression models. Children reported consuming, on average, 746 kcal during school hours (one-third of their daily energy intakes). Vitamins A, D, B 12 , calcium, and dairy products densities were at least 20% lower during school hours compared with non-school hours. Differences in School-HEI scores were poorly explained by sociodemographic factors, although age and province of residence emerged as significant correlates. The school context provides an important opportunity to promote healthy eating, particularly among adolescents who have the poorest school-hour dietary practices. The nutritional profile of foods consumed at school could be potentially improved with increased intake of dairy products, thereby increasing intakes of protein, vitamin A, vitamin D, calcium, and magnesium.